A drill chuck such as described in U.S. Pat. No. 4,836,563 for use with a tool having a shaft typically has a chuck body centered on and rotatable about an axis and an adjustment body centered on the axis, rotatable about the axis on the chuck body, and axially fixed on the chuck body. One of the bodies is formed with a plurality of angularly equispaced jaw-guide passages centered on respective jaw axes all lying on the surface of an imaginary cone centered on the axis. The other of the bodies is formed with a screwthread centered on the axis and exposed in the guide passages. Respective jaws displaceable in the passages along the respective axes are each formed with a row of teeth meshing with the screwthread so that relative rotation of the bodies in one direction moves the jaws radially inward an axially forward and opposite relative rotation moves the jaws radially outward and axially rearward.
Such a chuck is often set up to be self-tightening by forming the passages in the adjustment body and is provided with a locking ring that is axially and limitedly angularly displaceable on the chuck body and engageable with teeth on the adjustment body to limit its rotation. As the chuck is used the torque imparted to it tends to screw down the jaws, tightening them on the tool.
In order that the locking ring not interfere with the self-tightening action, it is necessary that the locking ring be limitedly rotatable on the chuck to follow the rotation of the element that rotates as the chuck self tightens. Two end stops are provided as described in U.S. Pat. No. 4,773,657 and a spring arrangement that normally returns the locking ring to the so-called starting end position corresponding to the position from which it will move as the chuck self tightens. To this end the locking ring is formed with two axially extending short and long grooves and the chuck body has a head that projects into them. In one end position the head is in the long groove so that teeth on the front end of the locking ring engage the adjustment sleeve and prevent it from rotating and in the other position the head is in the short groove and the locking-ring and adjustment-sleeve teeth do not engage. The locking ring can be pulled back against the force of a spring to allow the position to be selected.
In German patent 3,093,443 of H. Mack a system is described where the jaws are carried by the adjustment sleeve. To establish the two end positions of the locking ring the chuck body has two axially extending planar surfaces confronting respective surfaces of the locking ring. Similarly, U.S. Pat. No. 4,836,563 has a system where the two end positions are established by a recess in the locking ring and a pin projecting into this recess and seated in the chuck body. Thus once again the locking ring can assume two angular end positions and two different axial positions.
With the known lockable self-tightening chucks it is essential that the locking ring be set in its starting end position. Otherwise the locking ring will inhibit self-tightening of the chuck. It is also of course essential that the locking ring be set in the position permitting it to move axially forward for locking action. Hence the locking ring must be exactly set each time a bit is fitted to the chuck to ensure both locking and self-tightening action. If the tool operator does not do this carefully, these functions of the chuck are lost.